London: Many smokers reach for a cigarette to ease their anxiety during stressful periods. But US researchers have found that quitting smoking makes people happier, and the effect lasts for as long as they manage to kick the habit.

The team from Brown University and the University of Southern California said it showed quitting is not, as many smokers fear, a psychological sacrifice made for the sake of their physical health.

Study author Christopher Kahler from Brown University said: "If people quit smoking their depressive symptoms go down and if they relapse, their mood goes back to where they were. An effective anti-depressant should look like that," a newspaper reported.

The researchers studied a group of 236 men and women who were trying to quit the habit. They received nicotine patches and counselling and agreed to a quit date, according to a Brown statement.

Then were then tested for depressive symptoms a week before the quit date and then two, eight, 16 and 28 weeks after that date.

Nearly half of the subjects, who never managed to abstain from smoking, remained the unhappiest throughout the study.

A fifth only quit up to the two-week assessment while around one in six managed to stay off cigarettes until the eight-week assessment and the same proportion kicked the habit for the whole study.

The scientists found those who quit and stuck with abstinence were the happiest to begin with, and this elevated mood remained constant throughout.

Those who quit temporarily were happy while they were not smoking, but their mood darkened significantly when they gave into temptation.

Kahler said he was confident the results apply to most people, even though the smokers in this study were also heavy drinkers.